Many flowable products, such as certain foods, cosmetics and pharmaceuticals have a tendency gradually to spoil or deteriorate upon contact with the ambient atmosphere. This is primarily due to the oxygen and water vapor (hereinafter collectively referred to as "oxygen") contained in the atmosphere which have a deleterious effect on the products. Even if such flowable products are not completely spoiled, they oftentimes, upon prolonged contact with the atmosphere, assume a dry or crusty condition at their exposed surfaces which renders dispensing of the products more difficult, if not impossible.
In recent years a variety of so-called "barrier" materials has been proposed for use in container walls. These barrier materials render the container walls substantially impervious to oxygen or at least substantially reduce the penetration of oxygen into the interior of the container. Some of the many known barrier compositions are disclosed in the prior art referred to above. However, prior art container structures with barrier characteristics are relatively rigid and thick-walled. Attempts to provide such containers with flexible, relatively thin wall structures having satisfactory barrier characteristics have failed, since upon repeated flexing, the container walls tend to develop micro-cracks which, of course, reduce the barrier capability of the wall structure, thereby negating the barrier effect. This holds particularly true if the container is of the collapsible pleated or bellow type, such as disclosed in U.S. Pat. No. 3,506,163.
Pleated containers are usually manufactured from a prefabricated extruded parison or tubular plastic body which by way of blow molding, is formed into the pleated container shape. Since the parison has a uniform cross-sectional thickness, the thickness of the container at and near the extremities of the pleats is reduced as compared to the thickness at the remaining portions of the pleats. This is so because in the blow molding procedure, the wall forming parison material gradually thins out or necks down towards the extremities of the pleats, the thinnest wall portion being at the outer apexes of the pleats. If the parison contains barrier material, the amount of barrier material is then insufficient at the thin extremities of the pleats effectively to prevent penetration of oxygen into the interior of the container.
The terms "pleated" or "bellows" as used herein refers to containers that are flexible in one direction but substantially rigid in the direction transverse to said one direction and include containers wherein the pleats or bellows collapse when sufficient product has been dispensed.